In conventional wells for the production of hydrocarbons, one or more cylindrical casings surround a smaller diameter production tubing through which the hydrocarbons will flow to the wellhead. Production tubing conventionally consists of discrete lengths of steel tubing threaded together end-to-end to form a production string extending downhole from the wellhead to the zone or zones of hydrocarbon concentrations. The insertion and periodic removal of the production tubing for well servicing purposes was and is a time consuming and therefore expensive process due to the time and equipment needed to make or break the connections in the string and to store the discrete lengths of tubing when not in use.
Similarly, several types of well workovers, such as cleanouts, require that the production tubing be removed and replaced with service tubing. The same problems mentioned above in relation to production tubing are encountered if the service tubing similarly consists of discrete lengths of metal pipe threaded together end to end.
More recently, continuous tubing has been developed that is capable of storage on a reel much like rope and that has facilitated a much speedier and more economical means of injecting or removing the tubing using specialized service rigs. Typically enough tubing can be stored on a single reel to eliminate the need for any pipe connections and this greatly speeds the injection and withdrawal steps.
In the downhole coiled tubing service industry, the conventional method of guiding the tubing from the roughly horizontal or upwardly sloping direction of the tubing coming off the spool to the vertical direction required for downhole injection is accomplished using a roller-type tubing guide arch. Such arches typically include a plurality of spaced apart rollers placed at discrete intervals around the curvature of the arch for supporting the tubing passing thereover. The spacing of these rollers and their small diameter in relation to the bend radius of the tubing contributes significantly to stress and fatigue in the tubing by forcing it to bend more sharply as it passes over each roller. The tension in the tubing string due to its own weight and resistance to being uncoiled pulls the tubing forcefully against each roller thereby inducing excessively high contact stresses in the tubing due to the very small roller surface area in contact with the tubing passing thereover. This then leads to shortened tubing life and more frequent failure in the string due to a concentration of bending moments and the problems caused thereby.